Paper feed roller

ABSTRACT

Provided is a paper feed roller in which paper conveyance failure is suppressed over a long period of time. The paper feed roller is a paper feed roller 10 including a shaft body 12 and an elastic body layer 14 formed on an outer periphery of the shaft body 12. A plurality of convex portions 16 forming surface unevenness is arranged on a peripheral surface of the elastic body layer 14. The contact area of the entire parts in contact with a glass surface when a glass plate is pressed against the peripheral surface of the paper feed roller 10 with a load of 0.5 to 2.3 N per centimeter in an axial direction is 1.0 to 15% of the nip area with the glass surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of International Application number PCT/JP2019/016118 on Apr. 15, 2019, which claims the priority benefit of Japan Patent Application No. 2018-086083, filed on Apr. 27, 2018. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

The present disclosure relates to a paper feed roller that is suitably used in an electrophotographic device such as a copying machine, a printer, or a facsimile which employs electrophotography.

Related Art

The paper feed roller is formed into a cylindrical shape by an elastic material such as a rubber cross-linked body, and a peripheral surface thereof serves as a contact surface with the paper. Paper dust generated from the paper may adhere to the peripheral surface of the paper feed roller. Then, during repeated contact with the paper, paper dust may accumulate on the peripheral surface of the paper feed roller. When the paper dust is accumulated, the contact area of the peripheral surface with respect to the paper is reduced, and the friction coefficient of the contact surface with respect to the paper is reduced. As a result, paper conveyance failure may occur.

It is known that unevenness is formed on the peripheral surface of the paper feed roller in order to suppress paper conveyance failure (Patent literature 1). For example, Patent literature 1 describes a paper feed roller having a plurality of ridges and grooves formed in parallel with the axial direction of the paper feed roller.

LITERATURE OF RELATED ART Patent Literature

-   Patent literature 1: Japanese Patent Laid-Open No. 2017-65907

Conventional paper feed rollers are still insufficient in maintaining a good friction coefficient from the beginning of use for a long period of time. In particular, among the paper used in recent years, there is low-quality paper which is likely to generate paper dust, and paper conveyance failure is likely to occur at a relatively early stage.

The problem to be solved by the present disclosure is to provide a paper feed roller that suppresses paper conveyance failure over a long period of time.

SUMMARY

The paper feed roller according to the present disclosure for solving the above-mentioned problems is a paper feed roller for electrophotographic device and has a shaft body and an elastic body layer formed on an outer periphery of the shaft body. A plurality of convex portions forming surface unevenness is arranged on a peripheral surface of the elastic body layer, and the contact area of the entire parts in contact with a glass surface when a glass plate is pressed against the peripheral surface of the paper feed roller with a load of 0.5 to 2.3 N per centimeter in an axial direction is 1.0 to 15% of the nip area with the glass surface.

In the paper feed roller according to the present disclosure, in one of the exemplary embodiments, the ratio of the contact area per convex portion is 0.02 to 10% in the entire parts in contact with the glass surface. In addition, in one of the exemplary embodiments, the plurality of convex portions is regularly arranged on the peripheral surface of the elastic body layer. Besides, the plurality of convex portions may consist of two types of convex portions having different heights. In this case, the height of the low convex portions is preferably 70 to 80% of the height of the high convex portions in the two types of convex portions having different heights.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic external view of a paper feed roller according to an embodiment of the present disclosure.

FIG. 2 shows examples of the shape of a plurality of convex portions arranged on a peripheral surface of an elastic body layer of a paper feed roller.

FIG. 3 shows examples of arrangements of a plurality of convex portions arranged on the peripheral surface of the elastic body layer of the paper feed roller.

FIG. 4 is a diagram showing a method of obtaining an area ratio of actual contact parts when a glass plate is pressed against a peripheral surface of a paper feed roller.

FIG. 5 is an observation photograph of a nip portion when a glass plate is pressed against the peripheral surface of the paper feed roller of Example 1.

DESCRIPTION OF THE EMBODIMENTS

According to the paper feed roller of the present disclosure, the contact area of the entire parts in contact with the glass surface when the glass plate is pressed against the peripheral surface of the paper feed roller with a load of 0.5 to 2.3 N per centimeter in the axial direction is 1.0 to 15% of the nip area with the glass surface, and by reducing the contact area with the glass surface, the contact area with the paper during paper conveyance becomes smaller. Therefore, the amount of paper dust generated due to paper scraping is suppressed. In addition, because the contact area with the paper is small, the paper dust generated during paper conveyance immediately moves from the convex portions of the roller surface to the concave portions, and the reduction in the friction coefficient caused by the paper dust staying in and adhering to the contact parts with the paper is suppressed. Accordingly, paper conveyance failure can be suppressed for a long period of time.

Besides, when the ratio of the contact area per convex portion is 0.02 to 10% in the entire parts in contact with the glass surface, the contact area of one convex portion with the paper during paper conveyance is also small, and thus the amount of paper dust generated due to paper scraping and the reduction in the friction coefficient can be further suppressed. Besides, when a plurality of convex portions is regularly arranged on the peripheral surface of the elastic body layer, continuous grooves of concave portions are formed in the arrangement direction, the grooves serve as a discharge path for the paper dust generated during paper conveyance and the paper dust is easily discharged to the outside of the roller. Therefore, the reduction in the friction coefficient due to the accumulation of the paper dust can be suppressed. Besides, when the plurality of convex portions consists of two types of convex portions having different heights, the high convex portions mainly bears the load of the entire roller, and thus the load on the low convex portions can be reduced and the contact area of the entire roller with the paper is easily reduced. Further, because the low convex portions also contribute to the paper conveyance even if the contact load is small, it is easy to secure the paper conveyance force and suppress paper conveyance failure.

A paper feed roller according to the present disclosure (hereinafter, also simply referred to as paper feed roller) is described in detail. FIG. 1 is a schematic external view of a paper feed roller according to an embodiment of the present disclosure.

A paper feed roller 10 according to an embodiment of the present disclosure includes a shaft body 12 and an elastic body layer 14 formed on the outer periphery of the shaft body 12. The elastic body layer 14 is a layer (outermost layer) that appears on the surface of the paper feed roller 10. The elastic body layer 14 has a tubular shape (cylindrical shape). On the peripheral surface of the elastic body layer 14, a plurality of convex portions 16 that forms surface unevenness is arranged. Concave portions lower than the convex portion 16 exist between the convex portions 16 and the peripheral surface of the elastic body layer 14 becomes uneven due to the plurality of convex portions 16.

In order that the contact area with the paper becomes small when the paper is conveyed, the contact area (the total area of the actual contact parts) of the entire parts in contact with a glass surface when a glass plate is pressed against the peripheral surface of the paper feed roller 10 (here, the peripheral surface of the elastic body layer 14) with a load of 0.5 to 2.3 N per centimeter in the axial direction is 1.0 to 15% of the nip area with the glass surface. The nip area is the area of the entire nip portions serving as regions that are recessed when the glass plate is pressed against the peripheral surface of the paper feed roller 10, and the contact area is the entire area of the portions of the entire nip portions that actually contact the glass surface. By reducing the contact area with the glass surface, the contact area with the paper at the time of paper conveyance is reduced, and thus the amount of paper dust generated due to paper scraping is suppressed. In addition, due to the small contact area with the paper, the paper dust generated during the paper conveyance immediately moves from the convex portions of the roller surface to the concave portions, and the reduction in the friction coefficient caused by the paper dust staying and adhering to the contact parts with the paper is suppressed. Accordingly, paper conveyance failure is suppressed for a long period of time. The contact area is more preferably within the range of 3.0 to 12% of the nip area, and further preferably within the range of 5.0 to 12% of the nip area.

The percentage of the above contact area (the total area of the actual contact parts) can be obtained by observing, under a microscope, a predetermined range at the nip portion when the glass plate is pressed against the peripheral surface of the paper feed roller 10 with a predetermined load. The ratio of the contact area (the total area of the actual contact parts) can be adjusted by the shape of the convex portions, the density of the convex portions, the elasticity (material) of the convex portions, and the like.

In the paper feed roller 10, a small ratio of the contact area per convex portion to the entire portion in contact with the glass surface is preferable. Because the contact area of each convex portion with respect to the paper at the time of paper conveyance is small, the amount of paper dust generated due to paper scraping and the reduction in the friction coefficient is further suppressed. From this viewpoint, the ratio of the contact area per convex portion is preferably 0.02 to 10% and more preferably 0.1 to 5%. The ratio of the contact area per convex portion (the area of the actual contact part) can be obtained by observing, under a microscope, a predetermined range at the nip portion when the glass plate is pressed against the peripheral surface of the paper feed roller 10 with a predetermined load.

The plurality of convex portions 16 may be formed of convex portions having the same height or may be formed of convex portions having different heights. When the plurality of convex portions 16 consists of two types of convex portions having different heights, the high convex portions mainly support the load of the entire roller, and thus the load on the low convex portions can be reduced and it is easy to reduce the contact area of the entire roller with the paper. In addition, since the low convex portions contribute to the paper conveyance even if the contact load is small, it is easy to secure the paper conveyance force and suppress paper conveyance failure. In this case, the height of the low convex portions of the two types of convex portions having different heights is preferably 70 to 80% of the height of the high convex portions.

The height of the convex portions 16 is not particularly limited and is preferably in the range of 0.02 to 0.40 mm. When the height of the convex portions 16 is 0.02 mm or higher, the volume of the concave portions between the convex portions 16 becomes large, and the generated paper dust is unlikely to be clogged in the concave portions. From this viewpoint, the height of the convex portions 16 is more preferably 0.05 mm or more. In addition, when the height of the convex portions 16 is 0.40 mm or lower, the diameter of the bottom of the convex portions 16 can be appropriately kept small, and thus the dispersibility of the convex portions 16 is improved and the effect of pressure dispersion on the paper is improved. Accordingly, the generation of paper dust is easily suppressed. From this viewpoint, the height of the convex portions 16 is more preferably 0.30 mm or lower.

In FIG. 1, the convex portions 16 are hemispherical convex portions. The spherical shape may be a substantially spherical shape and have a shape close to a spherical shape having a curved surface. The spherical shape includes a true spherical shape and an elliptic spherical shape. A hemisphere includes a shape of a half of a sphere that is cut along a plane that passes through the center of the sphere, and a shape that is larger or smaller than half of a sphere that is cut along a plane that does not pass through the center of the sphere.

In FIG. 1, the plurality of convex portions 16 is uniformly distributed and disposed on the peripheral surface of the elastic body layer 14. The plurality of convex portions 16 may also be randomly disposed on the peripheral surface of the elastic body layer 14 or may be disposed so as to be arranged.

In FIG. 1, the plurality of convex portions 16 is disposed on the peripheral surface of the elastic body layer 14 so as to be arranged in the axial direction and the peripheral direction. Continuous concave grooves exist between the rows of the convex portions 16 arranged in the peripheral direction. In addition, continuous concave grooves also exist between the rows of the convex portions 16 arranged in the axial direction. Because the grooves of the concave portions which are continuous in the peripheral direction are formed in the rotation direction of the paper feed roller 10, the paper dust that has moved from the convex portions 16 to the grooves of the concave portions is easily discharged, along with the rotation of the roller, from the grooves to the outside of the roller without staying in the grooves. That is, because the grooves serve as a discharge path for the paper dust generated when the paper is conveyed and the paper dust is easily discharged to the outside of the roller, the reduction in the friction coefficient due to the accumulation of the paper dust is easily suppressed.

The shape of the plurality of convex portions arranged on the peripheral surface of the elastic body layer 14 is not limited to the hemispherical convex portions 16 shown in FIG. 1 and may have various shapes. The shape of the convex portion may be an irregular shape, a columnar body shape, a tapered body shape, a spherical base shape, a wedge shape and the like. The columnar body may be a cylindrical body, an elliptical columnar body, a prismatic columnar body (a square columnar body, a pentagonal columnar body, etc.), a fan-shaped columnar body, a D-shaped columnar body, and a gear-shaped columnar body. Further, the columnar body may be a truncated columnar body (a truncated cylindrical body, a truncated prismatic body, etc.) having a shape in which the head of the columnar body is cut into a slope shape or a curved surface shape.

The tapered body may be a cone, an elliptical cone, a pyramid (a quadrangular pyramid, a pentagonal pyramid, etc.). Further, the tapered body may be a truncated tapered body (a truncated cone, a truncated pyramid, etc.) having a shape in which the head of the tapered body is cut into a plane (frustum), a slope, or a curved surface. The spherical base is a solid shaped like a sphere cut out by two parallel planes. When a sphere surface intersects two parallel planes, the portion of the sphere surface sandwiched between the two planes is a spherical zone, and the solid surrounded by the spherical zone and the two planes is a spherical base. One of the two planes of the spherical base may be a surface passing through the center of the sphere, or both of the two planes of the spherical base may be surfaces not passing through the center of the sphere. The two planes of the spherical base may be a surface close to a plane, for example, a curved surface having a larger radius of curvature than the spherical zone. In addition, each upper bottom (upper plane) of the cylindrical body, the elliptic columnar body, the prismatic columnar body, the fan-shaped columnar body, the D-shaped columnar body, the gear-shaped columnar body, the frustum and the spherical base may be a polished surface. The polished surface can be formed by polishing each upper bottom.

FIG. 2 shows examples of the shape of the plurality of convex portions arranged on the peripheral surface of the elastic body layer 14. (a) of FIG. 2 shows a convex portion 161 having a shape (a truncated cone shape) in which the head of a cone is cut off by a plane parallel to the bottom surface. (b) of FIG. 2 shows the hemispherical convex portion 16 shown in FIG. 1. (c) of FIG. 2 shows a cylindrical convex portion 162. (d) of FIG. 2 shows a convex portion 163 having a rectangular prism shape. (e) of FIG. 2 shows a convex portion 164 having a shape (quadrangular pyramid trapezoidal shape) in which the head of a quadrangular pyramid is cut out by a plane parallel to the bottom surface.

The plurality of convex portions arranged on the peripheral surface of the elastic body layer 14 may be formed of only one type of these various convex portions, or may be formed by combining two or more types. For example, the peripheral surface of the elastic body layer 14 of one paper feed roller 10 may include hemispherical convex portions 16 and truncated cone-shaped convex portions 161.

The plurality of convex portions arranged on the peripheral surface of the elastic body layer 14 may be arranged in an arrangement form other than the arrangement form shown in FIG. 1. FIG. 3 shows other arrangement forms of the plurality of convex portions.

In the paper feed roller 20 of (a) of FIG. 3, the plurality of convex portions 16 is arranged in a staggered pattern on the peripheral surface of the elastic body layer 14. Specifically, the convex portions 16 of the second row are disposed between the convex portions 16 of the first row, the convex portions 16 of the third row are disposed between the convex portions 16 of the second row, and the convex portions 16 of the fourth row are disposed between the convex portions 16 of the third row, the convex portions 16 being arranged in an alternating manner. In the paper feed roller 20 of (a) of FIG. 3, the plurality of convex portions 16 is particularly uniformly disposed on the peripheral surface of the elastic body layer 14. For this reason, the contact with the paper becomes particularly uniform when the paper is conveyed.

In the paper feed roller 30 of (b) of FIG. 3, on the peripheral surface of the elastic body layer 14, the convex portions 16 are arranged (in the direction of the arrow) along a direction of a predetermined angle of less than 45° with respect to the axial direction (an oblique direction close to the axial direction). The paper feed roller 30 of (b) of FIG. 3 has a configuration in which a plurality of rows of the convex portions 16 in the direction of a predetermined angle is lined up. In the paper feed roller 30 of (b) of FIG. 3, since the grooves of the concave portions between the rows of the convex portions 16 are formed in the direction of a predetermined angle less than 45° with respect to the axial direction (an oblique direction close to the axial direction), the paper dust generated when the paper is conveyed easily moves from the convex portions 16 of the roller surface to the grooves of the concave portions, the paper dust hardly stays in and adheres to the contact parts with the paper, and the reduction in the friction coefficient due to the staying and adhering of the paper dust is easily suppressed.

In the paper feed roller 40 of (c) of FIG. 3, on the peripheral surface of the elastic body layer 14, the convex portions 16 are arranged along a direction of a predetermined angle of more than 45° with respect to the axial direction (an oblique direction close to the peripheral direction). The paper feed roller 40 of (c) of FIG. 3 has a configuration in which a plurality of rows of the convex portions 16 arranged around in the direction of a predetermined angle is lined up (not in a spiral shape) on the peripheral surface of the elastic body layer 14. In the paper feed roller 40 of FIG. 3(c), because the grooves of the concave portions between the rows of the convex portions 16 are formed in the direction of a predetermined angle of more than 45° with respect to the axial direction (an oblique direction close to the peripheral direction), the paper dust that has moved from the convex portions 16 to the grooves of the concave portions is easily discharged, like the grooves of the concave portions continuous in the peripheral direction in FIG. 1, from the grooves to the outside of the roller without staying in the grooves as the roller rotates. That is, the grooves serve as a discharge path for the paper dust generated when the paper is conveyed and the paper dust is easily discharged to the outside of the roller, and thus the reduction in the friction coefficient due to the accumulation of the paper dust is easily suppressed.

In the paper feed roller 50 of (d) of FIG. 3, on the peripheral surface of the elastic body layer 14, the convex portions 16 are arranged along a direction of a predetermined angle of more than 45° with respect to the axial direction (an oblique direction close to the peripheral direction). The paper feed roller 50 of (d) of FIG. 3 has a configuration in which the convex portions 16 are spirally arranged in a direction of a predetermined angle on the peripheral surface of the elastic body layer 14. In the paper feed roller 50 of (d) of FIG. 3, the convex portions 16 are arranged as shown by the dotted line on the other side of the paper surface. Similar to the paper feed roller 40 of (c) of FIG. 3, the paper dust that has moved from the convex portions 16 to the grooves of the concave portions is easily discharged from the grooves to the outside of the roller without staying in the grooves as the roller rotates.

Next, the material constitution of the paper feed roller according to the present disclosure is described.

A metal core made of a solid metal body, a metal cylindrical body being hollow, or the like is used as the shaft body 12. The material of the shaft body 12 may be stainless steel, aluminum, plated iron and the like. Moreover, an adhesive, a primer or the like may be applied to the shaft body 12 as necessary, and the adhesive, the primer or the like may be made electrically conductive as necessary.

The elastic body layer 14 is formed of an elastic material such as a cross-linked material of rubber. The material is not particularly limited as long as it is a rubber-like elastic material. For example, known rubber materials such as urethane rubber, hydrin rubber and silicone rubber can be used.

The elastic body layer 14 preferably has conductivity or semiconductivity. Specifically, the volume resistivity of the elastic body layer 14 is preferably in the range of 10² to 10¹⁰ Ω·cm, 10³ to 10⁹ Ω·cm, 10⁴ to 10⁸ Ω·cm. When the elastic body layer 14 has conductivity or semiconductivity, the surface residual charge of the elastic body layer 14 is kept low and the adhesion of the paper dust is suppressed easily.

The elastic body layer 14 may include a conductive agent from the viewpoint of lowering electrical resistance. The conductive agent may be an electronic conductive agent or an ionic conductive agent. The electronic conductive agent may be carbon black, graphite, c-TiO₂, c-ZnO, c-SnO₂ (c-means conductivity) and the like. The ionic conductive agent may be quaternary ammonium salts, borate salts, surfactants and the like.

The elastic body layer 14 may be appropriately added with various additives if necessary. The additives may be a lubricant, a vulcanization accelerator, an anti-aging agent, a light stabilizer, a viscosity modifier, a processing aid, a flame retardant, a plasticizer, a filler, a dispersant, a defoamer, a pigment, a release agent, and the like.

The thickness of the elastic body layer 14 is not particularly limited and may be appropriately set within a range of 0.1 to 10 mm.

The elastic body layer 14 can be formed using a rubber composition by, for example, molding with a molding die. For example, the shaft body 12 is coaxially installed in the hollow part of the roller molding die, and an uncrosslinked rubber composition is injected, heated, cured (crosslinked), and then released from the mold, thereby forming the elastic body layer 14 on the outer periphery of the shaft body 12. A molding die in which concave portions having a shape corresponding to the convex portions 16 are formed on the inner peripheral surface can be used. The convex portions 16 of the elastic body layer 14 can be formed, for example, by die transfer using the molding die.

The concave portions on the inner peripheral surface of the molding die can be formed by various concave portion forming methods such as electric discharge machining, etching, shot blast, polishing, eutectoid plating, combinations thereof, etc. In eutectoid plating, uniform resin particles are contained in the plating solution, the resin particles are deposited on the inner peripheral surface of the molding die together with the plating metal, and the resin particles appearing on the plating surface are removed, thereby forming concave portions on the inner peripheral surface.

The embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

For example, in the above-described embodiment, the paper feed roller 10 is configured to include the shaft body 12 and the elastic body layer 14 formed on the outer periphery of the shaft body 12, and the outermost layer is the elastic body layer 14. However, a surface layer may be arranged on the outer side of the elastic body layer 14. In this case, the surface layer is the outermost layer, and the elastic body layer 14 is arranged on the inner side of the surface layer. The convex portions 16 are formed on the peripheral surface of the elastic body layer 14, and the surface layer may be formed with a thickness that ensures the surface unevenness caused by the plurality of convex portions 16. Besides, a surface modification treatment may be performed instead of forming the surface layer.

EXAMPLE

Hereinafter, the present disclosure is described in detail with reference to examples and comparison examples.

Examples 1 to 17, Comparison Examples 1 to 4

An elastic body layer (thickness: 3 mm) of a urethane rubber composition was formed on the outer periphery of a core material (#6, made of SUS304) using a tubular molding die having a plurality of predetermined concave portions on the inner peripheral surface. Accordingly, a paper feed roller having a plurality of predetermined convex portions on the peripheral surface of the elastic body layer was obtained. The convex shape, the convex arrangement, and the convex height are shown in Tables 2 to 4. The correspondence between the convex shape and the drawing number and the correspondence between the convex arrangement and the drawing number are shown in Table 1 below. The irregular convex shape was formed using a tubular molding die in which the inner peripheral surface was subjected to electric discharge machining. The wavy convex shape was formed using a tubular molding die in which the inner peripheral surface was polished. Therefore, the irregular convex arrangement is arbitrary, and the wavy convex arrangement is also arbitrary.

TABLE 1 Convex shape FIG. number Irregular shape — Wavy — Truncated cone (a) of FIG. 2 Hemisphere (b) of FIG. 2 Cylinder (c) of FIG. 2 Prism (d) of FIG. 2 Pyramid (e) of FIG. 2 None — Vertical and horizontal FIG. 1 Staggered (a) of FIG. 3 Oblique (axial) (b) of FIG. 3 Oblique (peripheral) (c) of FIG. 3 Spiral (d) of FIG. 3

As shown in FIG. 4, a glass plate (50 mm×20 mm×2 mm) was pressed against the peripheral surface of the obtained paper feed roller 1 by the load shown in Tables 2 to 4, and the contact parts between the paper feed roller 1 and the glass plate 2 were observed with a microscope (“Laser Microscope VK9500” manufactured by Keyence Corporation). The observation range was 500 μm×300 μm, and the area ratio of the actual contact parts within that area was calculated. Further, the ratio of the contact area per convex portion in the entire actual contact parts was also calculated. FIG. 5 is an observation photograph of the nip portion when the glass plate is pressed against the peripheral surface of the paper feed roller of Example 1. The dark part is the actual contact part, and the light part is the non-contact part.

(Durability Evaluation)

The paper feed roller was incorporated into a commercially available copier with a FRR paper feed system, and paper feedability was evaluated. Commercially available PPC paper was used as the paper, 300,000 pieces of paper (300K pieces) were passed, and the number of paper jams due to paper dust was measured. “⊚” represents the paper feed roller in which paper jam occurred once or less, “∘” represents the paper feed roller in which paper jam occurred twice or more and five times or less, “x” represents the paper feed roller in which paper jam occurred six times or more and ten times or less, and “xx” represents the paper feed roller in which paper jam occurred 11 times. In addition, when the paper jam occurred 11 times, the durability evaluation was stopped.

TABLE 2 Example 1 2 3 4 5 6 7 8 9 Convex Irregular Irregular Irregular Wavy Truncated Truncated Truncated Truncated Truncated shape shape shape shape cone cone cone cone cone Convex None None None None Vertical Staggered Oblique Oblique Spiral arrangement and (axis) (peripheral) horizontal Convex type — — — — One One One One One Convex — — — — 0.20 0.20 0.20 0.20 0.20 height (high) (mm) Convex — — — — — — — — — height (low) (mm) Convex — — — — — — — — — height ratio (low/high) Ratio of 10 1.0 15 11 9 9 10 10 10 actual contact part % Ratio of one 0.1 to 1 0.02 to 0.2 to 10 0.2 to 0.1 0.1 0.1 0.1 0.1 convex % 0.1 2 Load (N/1 1.2 0.5 2.3 1.2 1.2 1.2 1.2 1.2 1.2 cm) Number of 3 2 4 5 2 0 2 0 0 paper jams (300K pieces) Judgment ◯ ◯ ◯ ◯ ◯ ⊚ ◯ ⊚ ⊚

TABLE 3 Example 10 11 12 13 14 15 16 17 Convex shape Hemisphere Column Prism Pyramid Truncated Truncated Truncated Truncated cone cone cone cone Convex Vertical Vertical Vertical Vertical Vertical None Vertical Vertical arrangement and and and and and and and horizontal horizontal horizontal horizontal horizontal horizontal horizontal Convex type One One One One Two One One One Convex height 0.20 0.20 0.20 0.20 0.20 0.20 0.05 0.50 (high) (mm) Convex height — — — — 0.16 — — — (low) (mm) Convex height — — — — 80% — — — ratio (low/high) Ratio of actual 10 10 10 10 12 10 9 9 contact part % Ratio of one 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 convex % Load (N/1 cm) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Number of 3 1 1 0 1 4 2 2 paper jams (300K pieces) Judgment ◯ ⊚ ⊚ ⊚ ⊚ ◯ ◯ ◯

TABLE 4 Comparison example 1 2 3 4 Convex shape Irregular Irregular Wavy Truncated shape shape cone Convex None None None Vertical and arrangement horizontal Convex type — — — Two Convex height — — — 0.2 (high) (mm) Convex height — — — 0.05 (low) (mm) Convex height ratio — — — 25% (low/high) Ratio of actual 0.8 16 20 18 contact part % Ratio of one — 0.3 to 5 0.4 to 10 0.1 convex % Load (N/1 cm) — 2.3   1.2 1.2 Number of paper jams — 7 11 (130k) 7 (300K pieces) Judgment — x xx x

According to the examples and comparison examples, it can be seen that when the contact area of the entire part in contact with the glass surface when the glass plate is pressed against the peripheral surface of the paper feed roller with a load of 0.5 to 2.3 N per centimeter in the axial direction is 1.0 to 15% of the nip area with the glass surface, paper conveyance failure can be suppressed for along period of time. In Comparison example 1, although the convex shape was adjusted so that the area ratio of the actual contact parts was 0.8%, when the glass plate was pressed with a load of 0.5 to 2.3 N per centimeter in the axial direction, the convex portions were crushed and could not be adjusted within the range of less than 1.0%. In Comparison examples 2 to 4, because the area ratio of the actual contact parts is in the range of more than 15%, there are many paper jams and it is not possible to suppress paper conveyance failure.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present disclosure. 

What is claimed is:
 1. A paper feed roller for electrophotographic device, comprising a shaft body and an elastic body layer formed on an outer periphery of the shaft body, wherein a plurality of convex portions forming surface unevenness is arranged on a peripheral surface of the elastic body layer, a contact area of the entire parts in contact with a glass surface when a glass plate is pressed against the peripheral surface of the paper feed roller with a load of 0.5 to 2.3 N per centimeter in an axial direction is 1.0 to 15% of a nip area with the glass surface, the ratio of the contact area per convex portion in the entire parts in contact with the glass surface is 0.02 to 10%, the plurality of convex portions is regularly arranged on the peripheral surface of the elastic body layer, the plurality of convex portions consists of two types of convex portions having different heights, and the height of the low convex portions is 70 to 80% of the height of the high convex portions in the two types of convex portions having different heights. 